Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known foil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
Utility grids typically operate at a constant frequency, in most cases approximately 50 or 60 Hertz. It is desirable that the electrical energy output from the wind turbine to the utility grid matches this frequency. However, due to the changing wind speeds that interact with the wind turbines, the input speed of the rotor blades and shaft is volatile and unpredictable, thus operating at a wide variety of frequencies different from the required constant frequency of the utility grid.
Various methods and apparatus have been utilized to facilitate a constant output from the wind turbine to the utility grid. For example, frequency converters have been provided between the generator of a wind turbine and the utility grid. However, the addition of this step in the production and transmittal of energy to the utility grid is both expensive and inefficient, and significantly contributes to the amount of downtime and repairs experienced by a typical wind turbine, thus reducing the overall effectiveness of the wind turbine and associated wind farm. Other solutions for facilitating a constant output include the addition of mechanical systems, such as differential gear assemblies, which account for changing wind speeds. However, such known mechanical systems typically interface directly with the output of the drivetrain. Such systems take on the full mechanical power, including torque and speed, of the drivetrain, and attempt to adjust the speed of the output by converting the torque to an attainable value and compensating with the necessary addition of torque to result in a desired speed. Such systems must therefore experience and attempt to counter output speeds caused by virtually the full power of the wind. The systems therefore require large, powerful components, such as hydraulics, which are expensive, or require large energy inputs, which defeat the purpose of the wind turbine.
Accordingly, an improved wind turbine drivetrain is desired in the art. In particular, a wind turbine drivetrain that facilitates a constant output to the electrical grid, and is reliable, efficient, and affordable, would be advantageous.